Manufacture of armor-plates and other articles.



UNITED sTAras RATENT OFFICE.

WILLIAM ARCHBOLD HARTLEY AND BEDFORD HENRY DEBY, OF SHEFFIELD, ENGLANDMANUFACTURE OF AIiMOR-PLATES AND OTIIER ARTICLES.

Specification of Letters Patent.

Patented April 27, 1909.

- Application filed July 10, 1908. Seria1'No.442,91 9.

Armor-Plates and other Articles, of which the following is aspecification.

This invention has for its object the manu factureof armor plates andother articles of a composite character, in which the face possessesextreme hardness and the remainmg portions are ductile and tenacious.

n the ordinary process of armor plate manufacture, the above conditionsare at tained by a differential heating and cooling,

so arranged that the face is raised to the hardening temperature whilethe remaining parts are kept much coole Afterward the face portion issprayed with cold water. This procedure has the disadvantage ofproducing unequal strains in the finished plate.

According to the present invention, un-

equal strains are obviated in the following manner:-It is known that inorder to in-" duce the maximum degreeof hardness in steel, it is.necessary'to heatgt'he' steel to a temperature in excessofthetransformation or critical oint of the steel; It is also known thatcertain classes of steel known as perlitic steels have two criticalpoints namel thatwhi'ch occurs on heating and that whic 1 occurs atrecalescence on cooling the latter being at a lower temperature than theformer. In this specification for the sake of clearness the former willbe termed the critical temperature and the latterv the temperature ofrecalescence. The present invention takes advantage of these facts by emloying a perlitic steel preferably one in whic there is a considerabledifference between the critical'temperature and the temperature ofrecalescence and then first heating that portion of the plate which isrequired to be hard, to a temperature" higher than the criticaltemperature ofthe steel, the remaining parts being ke t much below thiscritical temperature. ff now the hotter part of the plate be allowed tocool, the temperatureof the remaining portions being at the sametimeper-,

entirely immersed in; or sprayed with, a suitable chilling, liquid;after which the portion of the plate which had previously been heated toa temperature in excess of the critical temperature, will be hard, andthe remaining portions will be ductile and tenacious. Also on account ofthe equalized chilling temperature and uniform manner of chilling, all

dan erous strains will have been avoided.

\T iis process may be advantageouslyl employed with compound plates inwhic the initial ingot is cast in two or more successive layers, thechemical composition of the two layers being different and such that thecritical temperature of the face is considerably above that of the back.For instance the back of the plate may be cast of steel with a suitableproportion of nickel and chromium; immediately after the solidificationof this alloy, the face portionpreferably containing certain porportionsof molybdenum, chromium,-tungsten or other special hardening elements,is cast on to one side of it, thus insuring a sound interfusion freefrom imprisoned oxids etc. Thefollowingpercentages are suitable Face ofplate :Carbon .5 to 1.0%; chromium, tungsten or molybdenum, or any twoor all three, 1.0 to 3.0%; nickel 2.0 to 6.0%, Back of plate :'Garbon.10 to 30%; nickel 2% to 6%; chromium .75 to 3.0%; vanadium .25 to 1.0%separably or together. The compound ingot thus obtained is rolled,forged or pressed. The resulting plate is next heated to a hardeningtemperature and oil quenched. It is now reheated in such a manner thatthe de sired thickness of the face portion will reach a temperaturehigher than the critical temperature of either'of the alloys composinthe plate, the remainder of the plate being e t considerably below thattemperature; t e temperature of the face ortion is now al-' lowed tofall while that o theback is raised and the whole is-thus equalized at atemperature lower than the critical temperatures of the two alloys butabove the temperatures of. recalescence of the face; the plate is nowuniformly chilled,'either by immersion in, or

spraying with,,water or other suitable chilling medium. B this means thezone d viding the hardene from the unhardened portions of the face, isremoved away from the line ofinterfusion 'of the face" with the back;

alsoby finally chillingthe whole" of the plate,

are avoided. 9

11'0 .at a uniform temperature, unequal strains away from the line ofinterfusion of the face In carr ing out this invention use is made I ofa suitable vertical expanding ingot mold. The back ortion of the ingotis cast first, and imme iately after the solidification of 1 this alloy,the face portion is cast on to one side of it, thus insuring a soundinterfusion, free from imprisoned oxids etc. The com- E pound ingot thusobtained is rolled, forged or pressed. The resulting plate is next Iheated to a hardening temperature, 1'. e. i above 800 C. and oilquenched. It is now p reheated in such a manner that the desiredthickness of the face portion will reach a temperature hi her than thecritical teml peratures of eit er of the alloys composing 3 the plate,c. e. from 750 C. to 900 C. The remainder of the plate being keptconsiderably below those temperatures say at about 550 C. This mayconveniently be done by placing the plate face upward in a furnace I inwhich the flames can play direct upon the i face while the back andedges are protected by refractory material. The temperature of the faceortion is now allowed to fall while that of t e back is raised say bylifting the plate out of the protecting material, the temperature of thewhole being thus equal- I ized at a point lower than 750 C; the plate iis now uniformly chilled, either by immersion in, or' spraying with,water or other} suitable chilling medium. By this means the zonedividing the hardened from the unhardened portions of the face, isremoved with the back; also by finally chilling the whole of the plateat a uniform temperature, une ual strains are avoided.

hat we claim is 1. In the manufacture of articles such as i i l i l i il the remainder of the plate is kept considerably below thattemperature, then allowing the temperature of the face to fall andraising the temperature of the remainder in such a manner that thetemperature of the whole of the plate is equalized at a point lower thanthe critical temperature but above the temperature of recalescence andthen uniformly chilling the whole of the plate substantially asdescribed.

2. In the manufacture of articles such as armor plates which consists oftwo parts of differing composition, the face being of perlitic steelheating the plate in such a manner that a desired thickness of the faceportion reaches a temperature higher than the critical temperature ofeither alloy of which the plate is composed while the remainder of theplate is kept considerably below the critical temperature of eitheralloy, then allowing the temperature of the face to fall and raising thetemperature of the remainder in such a manner that the tern erature ofthe whole of the plate is equalize at a point lower than the criticaltemperature of either alloy but above the temperature of recalescence ofthe face and then uniformly chilling the whole of the plate,substantially as described.

WILLIAM ARCllliOhl) HARTLEY. BEDFORD HENRY DEBY. Witnesses:

LUTHER J. PARR, CHAs. N. DANIEL.

